Summary

This chapter discusses the underlying causes and consequences of reproductive skew in male primates. Although our understanding of the causes of skew is still in its infancy, empirical studies thus far support the compromise framework (e.g. tug-of-war model) rather than the concession model. Our assessment of the different models also suggests that the priority-of-access (POA) model makes predictions that are very similar to the compromise framework, but that skew models expand significantly on the POA model by including additional factors that relate to patterns of reproduction within groups. Our phylogenetic comparative analyses on mating skew in male primates also provide supporting evidence for the tug-of-war model, as mating skew decreased as the number of males increased, suggesting that monopolization of females becomes more difficult when there are more rivals (Emlen & Oring 1977). However, there have been no studies that represent strong tests of skew models, possibly because of difficulties in estimating parameters that are necessary for quantitative analyses. Future research could help to clarify the causes of skew, including development of mathematical models that are more suitable to primate societies, empirical studies based on paternity tests, and comparative approaches to investigate interspecific patterns of skew in other biological systems.

Previous studies commonly investigated the causes of skew, but fewer have considered the consequences of skew on other physiological and social parameters such as within-group relatedness and sexually transmitted diseases. Of these, it appears that effects on within-group relatedness could have the largest effects on patterns of primate sociality.